Scientists have developed an experimental vaccine to treat heroin addicts. Such a vaccine would be a major advance for both public health and safety. Addiction to the powerful, illicit narcotic not only destroys human lives, but also fuels a violent global drug trade.

An estimated 20 million people around the world are addicted to heroin and related opiates. Their addiction, and frequent use of contaminated syringes, put heroin users at risk of a variety of diseases - notably HIV/AIDS and Hepatitis C. They are also more likely to die prematurely, either from a drug overdose or the violence related to drug trafficking.

Drug relapse after conventional treatment for heroin addiction is an especially difficult challenge. The experimental vaccine may prevent addiction even if a user is re-exposed to the drug.

The heroin vaccine developed by Kim Janda and colleagues at the Scripps Research Institute in La Jolla, California essentially tricks the body's immune system into thinking heroin is a pathogen, like a bacterium or virus.

The experimental compound stimulates the production of antibodies that keep the drug from reaching the brain, which is where Janda notes the drug produces the euphoric high that heroin addicts crave.

"So, it creates like a wall to block the drug from entering the brain, the pleasure centers," said Janda. "And when it’s in circulation, our own body has enzymes that degrade heroin. And as it degrades it loses its ability to cross the blood-brain barrier, it loses its potency and eventually it’s just removed.”

Janda, a chemist and immunologist, says developing a vaccine against heroin has been especially challenging because the body rapidly metabolizes the drug into several byproducts, the last being morphine, the compound which actually triggers the high.

So, researchers had to develop a pretty versatile vaccine - one able to empower the immune system to recognize and produce antibodies that bind to all of the breakdown products before they reach the brain.

In experiments with heroin-addicted rats exposed to an unlimited supply of the drug, Janda says the results were striking. The drug-sated rodents were detoxified for one month, a period similar to a human going through drug rehabilitation.

Next, researchers divided the rats into two groups, again giving them as much heroin-laced water as they wanted. Only this time, Janda says half the rats had been vaccinated against heroin.

“What happens if you don’t vaccinate them [is] they re-escalate and double the amount of intake," he said. "In the case of the [rats given the] vaccine, they completely don’t recognize the heroin at all and stop taking it.”

None of the vaccinated rats relapsed after being re-exposed to heroin.

The National Institute on Drug Abuse, which has been interested in drug vaccine development, helped fund the research.

David Shurtleff, acting deputy director of the institute, says a heroin vaccine is not a "magic bullet" [complete cure] and would have to be used as part of a comprehensive treatment program that also addresses drug-seeking behavior. Like heroin-addicted humans who continue to crave the drug even after going through treatment, Shurtleff notes that the vaccinated rats persisted for a while in trying to get high.

"Once they are in an environment where they've been using the drug, they start to crave the drug and they will use it even though the vaccine may kick in to prevent the high," said Shurtleff. "They will still try and attempt to take the drug to overcome the craving, to reduce the craving for the drug. So, there's a lot of behavioral [elements] to addiction beyond what the vaccine can do."

Scripps investigators are currently seeking funding to begin human trials of the vaccine, possibly by later this year.

An article describing an experimental heroin vaccine is published in Proceedings of the National Academy of Sciences.